I. Field of the Invention
The present invention relates generally to the field of plowing snow, scraping ice, leveling gravel, and the like. More particularly, the present invention relates to an improved plowing system wherein a scraper is configured to quickly and retractably overcome obstacles that are encountered during such plowing, scraping, and leveling activities without the need for recharging or resetting the system pressure after the obstacles have been passed and which continually biases the scraper downward against the road surface such that the scraper will properly remove snow, sand, gravel, etc . . . from any dips or depressions in the road.
II. Discussion of the Prior Art
In the field of plowing and removing materials such as snow, ice, gravel, and the like, manufacturers have for years worked towards producing scrapers which are responsive and easily retractable so that the scrapers do not suffer damage when obstructions are encountered during such activities. U.S. Pat. No. 3,706,144 to Miceli represents one such attempt, disclosing a snow plow equipped with a pair of hydraulic angling cylinders for controlling the orientation of the plow relative to the front of the vehicle, a hydraulic lifting cylinder for controlling the vertical elevation of the plow, and various valve arrangements for selectively controlling the amount of oil that is distributed to the angling cylinders and lifting cylinder. In an effort to minimize the amount of damage experienced by the plow during plowing activities, steel coil springs are provided extending between the top of the plow and a frame member for allowing the plow to yield when obstacles are encountered. Although generally effective in preventing plow damage, a drawback exists in that the steel coil springs are fully exposed to the elements. This may cause the coil springs to stick due to the accumulation of snow and ice around or within the coils, in addition to causing the coil springs to rust and/or corrode due to the continued exposure to harsh plowing conditions.
Another approach to reducing the damage experienced by scrapers during road clearing activities resides in U.S. Pat. No. 3,893,518 to Farrell. In this patent, a plowing system is disclosed having a hydraulic cylinder and control system for selectively moving the plow between a raised position to a road contacting position. The system is charged at the onset of operations such that the hydraulic cylinder biases the plow into contact with the road surface. The hydraulic cylinder is further equipped with internally disposed spring means for automatically tripping the plow away from the road surface when the plow hits an obstruction and for automatically returning the plow into contact with the road surface when the obstruction is passed. While this arrangement obviates the problems attendant with the exposed spring members found in U.S. Pat. No. 3,706,144 to Miceli, a problem nonetheless exists in terms of the ability of the plowing system to accommodate immovable obstacles encountered while plowing. To be more specific, a pressure relief valve is employed which routes hydraulic fluid back into the reservoir when overpressure conditions exists or, in other words when the pressure within the hydraulic circuit exceeds a predetermined threshold. Such overpressure conditions exist when the plow hits an immovable object because the rearward motion of the plow causes a piston member within the hydraulic cylinder to displace and thereby forces hydraulic fluid out of the cylinder. Once the obstacle has been passed, the system operator must thereafter manually recharge the hydraulic cylinder to its predetermined pressure setting such that the plow returns to its originally biased state against the road surface. As will be readily appreciated, this need for manual operation is disadvantageously time consuming and furthermore may introduce inconsistency in the degree to which the plow is biased against the road surface.
U.S. Pat. No. 4,031,966 to Farrell represents yet another attempt at equipping a plow or scraper so as to yield to obstructions encountered while plowing. In this arrangement, a pair of cylinders operate with pressurized fluid and air to selectively move the plow between a raised position and a road contacting position, in addition to permitting the plow to yield when it engages a fixed obstacle in the road and return to the road contacting position when the obstacle has passed. The cylinders are first charged with pressurized air after which one of the cylinders is charged with pressurized hydraulic fluid. The hydraulic charge forces all of the air into the other cylinder and further compresses the air therewithin such that the compressed air biases the plow into contact with the road surface. While this approach is effective in alleviating the need for mechanical spring members, several formidable drawbacks still remain in the '966 patent which leave the field of endeavor in want of an improved plowing system.
One of the more pronounced defects in the '966 approach stems from the use of pressurized air in combination with pressurized hydraulic oil. To be more specific, this system is extremely dangerous in that it runs the risk of causing diesel combustion, which can result when air is charged to pressures above 200 p.s.i. and subsequently combined with hydraulic oil. This condition is a distinct possibility in that the step of charging the system with hydraulic oil further compresses the charged air from an initial level of 115 p.s.i. to a final level of approximately 575 p.s.i. As such, pressurized hydraulic fluid may leak or seep past the pistons into contact with the compressed air, thus raising the specter of diesel combustion. The potential for seal leakage is especially profound after prolonged periods of use when piston seals can become weakened and/or damaged. A further disadvantage resides in the fact that the system must be recharged prior to each individual plowing activity. As will be explained below, this results in increased response times for the operator to calibrate the system, in addition to cylinder damage over time. By way of background, each time a truck employing the plowing system of the '966 patent is started up the operator must manually open up an air valve to re-route compressed air from truck's air supply into the cylinders to charge the cylinders to approximately 115 p.s.i. This charging step serves to move the plow downwardly into engagement with the surface of the road and requires the operator to carefully control and monitor the degree to which air is introduced into the cylinder so that an air pressure of 115 p.s.i. is attained therewithin. Thereafter, the operator must manually operate the hydraulic valve manifold to charge the cylinders with hydraulic oil until the compressed air is further pressurized to approximately 575 p.s.i. Thus, the system of the '966 reference is disadvantageously time consuming in that each of the foregoing steps must be manually undertaken by the operator each time the truck is started in order to properly calibrate the system.
The '966 system is also flawed in that cylinder damage may result over time due to the attendant hydraulic foaming which tends to occur when the hydraulic oil is pumped from the reservoir. To be more specific, air bubbles are introduced into the hydraulic oil as the hydraulic oil is being pumped from the reservoir. These air bubbles are then transported within the hydraulic oil and introduced into the cylinders at great speeds, thereby resulting in intermittent rushes of oil and air which can be extremely harsh and damaging to the cylinders. In that cylinders are typically constructed from brass, which is relatively soft, the problem of hydraulic foaming is particularly ominous to the useful life of the system disclosed in the '966 patent, which, as noted above, requires recharging each time the truck is to be used for plowing.
Still another drawback of the '966 patent stems from the use of a 1500 p.s.i. pressure relief valve in between the pump and the hydraulic valve manifold. To further explain, trucks engaged in plowing activities are commonly equipped with several hydraulic implements, such as plows, hoists, underbody scrapers, and sanders, all of which are operated through the use of a single hydraulic circuit disposed within the truck. With the pressure relief valve disposed in between the pump and the valve manifold as disclosed, the maximum hydraulic pressure capable of being supplied to the various implements associated with the truck is limited to 1500 p.s.i. However, implements such as hoists and sanders typically require hydraulic pressures ranging between 2,000 p.s.i. to 3,000 p.s.i. for proper operation. With the hydraulic circuit limited to 1500 p.s.i., therefore, the device of the '966 patent is incapable of supplying adequate hydraulic pressure to these implements which require higher operating pressures, thereby curtailing the overall effectiveness of the truck. U.S. Pat. No. 4,074,448 to Niemela represents still another prior art plowing arrangement having the ability to avoid obstructions. The plow device of this reference boasts a dual construction with a vertically disposed hinge member joining a pair of blade sections, wherein the entire plow device is capable of yielding vertically away from the road surface upon hitting an obstruction and each individual blade section is capable of yielding horizontally rearward toward the truck upon hitting an obstruction. The ability to yield in the vertical plane is due to a horizontally disposed hinge unit which allows the plow to rotate about the horizontal hinge out of contact with the surface of the road when an obstacle is encountered. A spring-operated or pneumatically-operated biasing cylinder may be further provided to assist in returning the plow into contact with the road surface once the obstruction has been overcome. In order for the plow to yield in the horizontal plane, each blade section is equipped with either a bi-directional hydraulic cylinder, which is capable of both retracting and extending the individual blade sections, or a unidirectional hydraulic cylinder in combination with a biasing spring, which are used to retract and extend the blade sections, respectively. As with the previously discussed prior art plowing arrangements, a multitude of significant drawbacks similarly exist with the plowing device of the '448 reference.
With initial attention being directed to the vertical yielding feature of the '448 reference, the arrangement as disclosed is flawed in that it is possible for debris to become lodged between the opposing plates of the horizontal hinge member when obstructions are encountered. This stems from the fact that the opposing plates which comprise the horizontal hinge become separated when the plow encounters an obstruction while plowing. During the time that the horizontal hinge is in this separated condition, rocks and/or portions of ice and snow may be introduced between the opposing plates, thereby prohibiting the plates of the horizontal hinge from returning into flush contact with one another when the obstruction has been passed. This, in turn, may cause the plow to remain in an undesirable angled position or, worse yet, it may actually prohibit the plow from returning to the road surface even after the obstruction has been passed. Related problems may also result in terms of halting the plowing activities to clear the unwanted debris from within the compressed position between the plates of the horizontal hinge, which may be time consuming as well as dangerous.
Turning now to the horizontal yielding feature of the '448 device, this is also flawed due to the hydraulic system used to control each of the hydraulic cylinders which bias the blade sections in the extended position. To be more specific, a pressure relief valve is provided between the pump and each hydraulic cylinder (uni-directional or bidirectional) used to maintain the blade sections in the normal plowing position. Pressure relief valves are common in the art and basically serve as a safeguard to discharge hydraulic fluid from the pressure line back into the fluid reservoir during an overpressure condition within the pressure line. By positioning the pressure relief valve in between the pump and each hydraulic cylinder used to operate the blade sections, hydraulic fluid may be dumped back into the fluid reservoir when the blade sections yield rearwards upon encountering an immovable obstacle in the road surface. While the use of pressure relief valves in this fashion is effective in regulating overpressure conditions within the fluid lines which supply these hydraulic cylinders, a disadvantage exists in that the fluid pressure within the cylinders must be reset after each instance that the hydraulic fluid is forced back into the reservoir. As will be appreciated, the task of resetting or recharging the fluid pressure within the cylinders is time consuming in that the operator must manually operate a valve manifold to direct oil under pressure into the cylinders to return the cylinders to their normal operating pressure.
Based on the foregoing, it is apparent that a need exists for an improved plowing system which solves the aforementioned deficiencies in the prior art. Namely, a need exists for an improved plowing system which allows the plow or scraper to quickly and retractably overcome any obstacles that are encountered during plowing activities and which continually biases the scraper downward against the road surface such that the scraper will properly remove snow, sand, gravel, etc . . . from any dips or depressions in the road. Moreover, the improved plowing system should advantageously eliminate the need to recharge and recalibrate the hydraulic pressure within the system each time plowing operations are initiated, thereby decreasing the time required to prepare the truck for operation and decreasing the likelihood of cylinder damage. The improved plowing system should furthermore eliminate the potential for diesel combustion, in addition to providing the ability to simultaneously operate a plurality of hydraulic implements at a variety of different operating pressures. Additionally, the improved plowing system should allow the plow to yield upon hitting an obstacle without presenting the possibility that unwanted debris will prohibit the plow from returning to the proper position against the road surface.